As already noted all diseases which undermine the health tend to
diminish the powers of resistance to the tubercle bacillus. To be
especially dreaded, are long standing diseases which produce emaciation
and debility, fevers that for a length of time impair sanguification,
metabolism and nutrition, diseases of the digestive organs which cut off
the requisite supply of nutritive material, and, above all, diseases of
the lungs and air passages that impair the tone of the tissues and
invite the attack of the invading microbe. Bronchitis, laryngitis,
pharyngitis and tonsilitis in all their varied forms are to be
particularly noted. Even in man it is believed that one of the most
common channels of infection entrance is through the open tonsillar
crypts, and the same doubtless is true of animals. Pigs, with their
large tonsils and frequent infection through feeding, are probable
examples of this, and when, in addition to the detention of the microbe
in the cavities, there is an inflammation and debility of the tissues,
the opportunity for infection is greatly enhanced.